Cory Catfish: How to Buy, Care for, and Keep Them Healthy

In many ways, Corydoras are the dogs of the fishkeeping world:

They have loads of personality, they love to swim and play with each other, and they’re just all around fun to have in your fish tank.

Corys are also quite easy to take care of, regardless of whether you’re a beginner or a veteran aquarist.

(Plus, since they’re so popular, there is tons of information available to help diagnose problems and keep your corys healthy.)

But let’s cut to the chase.

Corys will tolerate a wide variety of tank conditions, but you should try to keep as close to the following as possible:

  • PH between 6.5-7.5 (See water conditions section below)
  • KH between 3-10
  • Temperature between 71.6-80F (Varies by type of cory, see water conditions section)

One thing to note: these are the preferred temperatures for corydoras, there are plenty of reports of people keeping their corys in water as low as 68F without any real issues for short periods.

There are also reports of these colder temperatures killing corys. Like this one:

As long as you keep to the above recommendations, you corys will have a good chance at thriving.

Let’s continue, however, because there are some mistakes you can make before even leaving your local fish store with your new corys.

How to Set Up Your Aquarium

Before I get to that, you need to know how to set up your aquarium.

You should ideally have the tank your corys will go into setup for 2 months before you add them in.

This allows beneficial bacteria to build up to a level that will actually be able to filter the ammonia and nitrite out of the water.

(There are products you can buy that claim to do this, but I’ve heard of quite a few people that used these “quick start” products and lost all the fish they put in within a week.)

This is the entire process:

Set Up Your New Tank

If you’re adding your corydoras into a new tank, set it up now and give it a chance to fully cycle. Slowly add food to create ammonia for the bacteria to feed on.

2 Months Later

Buy Your Corydoras

After about 8 weeks, the beneficial bacteria should be built up enough for your corys to be able to safely jump into your tank. If you already have an establish tank, jump to this step.

2 Months Later

Float Them in Your Tank

Float the bags your corydoras came in on top of your aquarium to allow the water temperatures to equalize gradually.

15 Minutes Later

Slowly Add Water

Open the top of the bag (or cut a slit at the top) and slowly add a 1/4 – 1/2 cup of water every 15 minutes. This will slowly adjust the PH in the bag to match your tank.

15 Minutes Later
2 Hours Later

Release Your Corydoras

Now you should be safe to release your corydoras into your tank. (Be sure to read about quarantine tanks below.)

2 Hours Later

Tank Size

A common mistake that many new fishkeepers make is choosing an aquarium that is too small for the number of fish they want to keep.

Corys like to have a lot of space to swim, so the smallest aquarium that I would recommend you keep corys in is a 20 gallon long aquarium.

(A regular 20g will hold as much water but will give them less room to swim.)

An aquarium this size should be good for a shoal of 8 pygmy corydoras.

(You may still be able to add some smaller fish such as guppies, tetras, or rasboras that swim higher up in the tank, but I would be careful about adding any more corys.)

For larger corys, you will want to upgrade to a 29 gallon. You’ll also want to upgrade if you plan on having more corys in the future. Bigger is almost always better in this regard.

If you get a 55 gallon aquarium, for example, you can handle 20-25 corys plus other types of fish that swim higher up in the tank.

A Habitat for Your Corydoras

Catfish Corydoras in an aquarium close up

When setting up your tank, you need to take your corys’ habits into consideration.

Namely:

  • To feel safe, they need to have places to hide.
  • They love sifting through the substrate looking for food.

What does this mean?

First, you need to have a tank that’s well planted out. Having a lot of plants will give them plenty of places to hide.

Don’t feel comfortable taking care of real plants?

You can use fake plants and other decorations, but make sure they’re not sharp and don’t have rough edges. Your corys’ whiskers (called barbels) are sensitive, and you don’t want them getting injured.

This brings us to the second point:

The ideal substrate for corydoras is a fine sand.

Corys love sifting through the substrate at the bottom of the aquarium. With gravel and other sharp or rough substrates, they can injure their barbels.

Check out a video of this cory sifting through aquarium sand in slow motion:

Water

As we covered in the intro, corydoras are tropical fish and prefer water in the range of 71.6-80F.

This table should give you an idea of what temperature you should keep each type of corydora at:

Corydora TypeIdeal Temperature Range
Most Corydoras71.6-80.6F
Bandit Corydoras71.6-78.8F
Black Fin Corydoras75-86F
Julii Corydoras77-82.4F
Panda Corydoras71.6-77F
Peppered Corydoras64.4-80.6F

Different corydoras may have different PH preferences based on their species or what PH they were kept in before, but a PH of 6.5-7.5 should be suitable for most of them. I’ve heard reports from various people that are keeping their corys in water all the way up to a PH of 8 without any issues.

That having been said, some can tolerate more acidic water as well:

Corydora TypeIdeal PH Range
Most Corydoras5.5-7.8
Adolfo Corydoras 5.6-7.2
Black Fin Corydoras5.6-7
Bandit Corydoras6.5-7.5
Dwarf Corydoras6.8-7.6
Gold Laser Corydoras6-7.5

Keep in mind:

Keeping your PH stable is more important than keeping your PH in the ideal spot.

Corys aren’t extremely fussy about their water conditions.

There is one thing you need to be concerned about, however:

Corys are extremely sensitive to nitrates.

(If you’re not familiar, fish produce ammonia as waste. Bacteria convert this into nitrite and then into nitrate. This leaves nitrate as a waste product in your aquarium water as a natural result of having fish.)

There are two things you can do to reduce the number of nitrates in your water:

  1. Water Changes. According to practical fishkeeping, you should change about 25% of your water every week. I’ve also heard suggestions of a 30% water change every 2 or 3 weeks.

    You should favor larger water changes less often over smaller water changes more often.
  2. Grow Live Plants. A lot of the waste products in the water (including nitrates) are actually nutrients for the plants growing in your aquarium. This means that as they grow, they are removing these waste products from the water, making the water safer for your fish.
Corydoras can survive in water between 71-80F and PH between 6-8.

Flow Rate

You’ve probably heard that betta and a lot of other fish don’t like any sort of current in their water, and that you should choose your filter to keep the water as calm as possible.

This is not the case for corydoras.

Corydoras are native to the rivers of South America, meaning they enjoy having a bit of a current in their aquarium.

One way you can make this happen is to have a powerhead on top of a sponge filter. This will provide filtration for your tank as well as providing a bit of a current for your corys to play in.

Be careful however:

Having too strong of a current throughout the entire tank can stress your fish.

You should always provide your fish areas that are still that they can rest in.

Oxygenation

Corydoras like having well oxygenated water.

There are a few things that you can do to increase the oxygenation in your water.

  1. Reposition Your Filter. Since most oxygenation takes place at the surface of your aquarium, you can increase the amount of oxygen your fish are getting by repositioning your filter to where it agitates the water at the top of your aquarium more.
  2. Buy an air pump. If you can’t adjust your filter, you can always install an air pump with an air stone. This is an easy way to increase the oxygen levels in your aquarium.

Buying Your Corydoras

Have your tank set up?

Great!

Now you’re ready to pick out your corys from your local fish store.

What to Look for When Buying a Cory Catfish

The last thing you want to do is bring home a sick cory from your LFS.

Luckily, there are a few things you can do to make sure you’re picking healthy ones.

A healthy Cory Catfish will be quite active and alert.

If you are looking at a Cory Catfish that appears very calm in the display tank, be wary.

Take a close look at the barbels (whiskers) on either side of its mouth. If these appear damaged, you might want to pick a different cory instead.

Their barbels are very sensitive and sometimes other fish in the tank will sometimes nip at them. This can (obviously) injure them, and you want to avoid taking one home that is already in bad condition at the store.

You also want to look for the following:

  • Red blotches (sometimes along with areas of messed up skin) can be an indication of the appropriately named red blotch disease.
  • White spots growing on a cory could be an indication of ich disease.
  • Ragged looking fins could mean the cory has fin rot.

If you see any of these, you should probably choose a different place to buy your corys from. These generally mean that your fish store isn’t taking proper care of their fish.

Painted Corydoras

There is a somewhat less common practice in the fishkeeping industry called ‘painting’.

This involves injecting a brightly colored dye into a fish using a hypodermic needle. This is done to give the fish a more striking appearance.

In most instances, if a cory has a bright red mark that runs along the lower back area, it has been injected with dye.

There is nothing inherently wrong with this, but this can increase the chances of infection significantly. (i.e. Dyed corys die more often.)

How Many Corydoras Should You Buy

School of Bronze corydoras swimming in aquarium tank,Corydoras aeneus

As I mentioned earlier, corys are a shoaling fish. This means they like to swim around in large groups.

Because of this, you should never buy just one cory for your tank.

If you want to keep corys, you need to buy at least 6 of them.

(Some sources say 5, but this is really a bare minimum number. Most reputable fish stores will recommend that you get at least 6.)

Keep in mind:

This is 6 of the same type of corydora.

For example, 6 panda corys would be appropriate. 3 bronze and 3 albino would not.

If you want to get multiple different types of corys, make sure that you get 6 of each type.

Introducing Your Corydoras Into Your Tank

A mistake a lot of people make is to just float the bag in the fish tank long enough to equalize the temperature and then release the fish into the tank.

This can be incredibly stressful on your new corydoras.

What you want to do instead is slowly (every 10-15 minutes) add ¼ cup of your fish tank’s water into the bag your new corys came in.

The goal here is to equalize the PH and other water conditions and make it easier for your new fish to transition into your aquarium.

If you have a PH tester, that will be the best way to tell when you’re done. Otherwise, repeat this process 6-8 times before releasing your new corys.

Quarantine

Have an established aquarium you’re planning on adding new corys into?

You may want to rethink that plan.

Any fish that you’re bringing in from an outside source could have any number of diseases or parasites.

If you just dump them into your main aquarium, you’ll be transmitting them to all of your other fish.

Nothing is worse than losing half of the fish in your tank because of something you brought in on a new fish.

Here’s what I recommend doing instead:

How to set up a quarantine tank

Set up a second tank (20G long should be fine), and place your new fish in there first.

Keep them there for 30-60 days, just to make sure they aren’t sick.

Once you’re confident that your new fish are healthy, move them over to your display tank.

Temperament

The Cory Catfish is a peaceful and non-aggressive fish.

They are quite active and enjoy swimming around the bottom of the tank in large groups.

What Should You Feed Your Corydoras?

Once we have our tank set up and our corydoras introduced, we need to know how to feed them.

Corydoras are omnivorous, but they lean heavily toward the carnivorous side of the spectrum.

This means that they require foods that are based primarily around meat (such as shimp) rather than plants or algae.

They also need foods that will sink to the bottom of the tank, as they are bottom feeders.

Some good options would be micro wafers (such as those produced by Hikari) or sinking shrimp pellets.

How Much Should You Feed Corydoras?

Each cory should be getting one sinking shrimp pellet or about 1/6th of a normal sized wafer.

This means if you have 6 corys, one normal sized wafer should be enough per day.

Like with any aquatic animal, you’ll want to vary what food you’re feeding them if possible. This will make sure they have a more complete diet.

Some of the other foods you can feed them a few times per week are frozen bloodworms, brine shrimp, and other similar whole prey.

What Fish Can You Keep With Corys?

Corydora with a pleco and rasbora

Some fish are jerks.

They’ll gladly kill your corys as soon as you turn your back.

To help you avoid this, I’ve compiled a list of fish that are safe to put your corys in with.

Safe fish:

  • Tetras
  • Guppies (and other live bearers)
  • Rasboras
  • Bristlenose Plecos (and other plecos as long as your tank is big enough)
  • Dwarf Cichlids (Avoid larger and more aggressive cichlids.)
  • Oto Catfish
  • Other small community fish

This is by no means an exhaustive list, but it should give you a good place to start.

In Conclusion

As you’ve seen, corydoras are easy fish to keep and don’t require a lot of special care or maintenance.

As long as you give them the right substrate, places to hide, and you don’t change their environment too drastically, you should be able to keep them happy for years.